Impact of body mass index on mortality in middle-aged Koreans: A prospective cohort study based on a Health Examinees study

Background: Obesity is the major cause of chronic diseases and the leading cause of mortality. We aimed to assess the impact of obesity on mortality in middle-aged Koreans using data from a Health Examinees study. Methods: We used data from 39,689 men and 76,272 women who had complete information on body size and gave informed consent for the linkage of their data with the national death certificate data. Cox proportional hazard model was used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of body mass index (BMI) for all-cause, cardiovascular, and cancer mortality. The educational level and habits of cigarette smoking, alcohol consumption, and regular physical activity were adjusted. The menopausal status was additionally adjusted in women. Results: We found increased risks of all-cause mortality among those with a BMI of < 18.5 kg/m 2 (adjusted HRs [95% CIs]: men, 2.24 [1.73–2.91]; women, 1.47 [0.98–2.22]) and 18.0–< 21 kg/m 2 (men, 1.18 [1.00–1]; women, 1.23 [1.01–1.50]) than in those with a BMI of 21–< 23 kg/m 2 . We also observed that men with BMIs of 23–< 25 kg/m 2 (0.85 [0.74–0.97]) and 25.0–26.9 kg/m 2 (0.87 [0.75-1.00]) had decreased risks of all-cause mortality. Conclusion: This large prospective study found significant associations between BMI and mortality. Especially, being underweight was associated with an increased risk of mortality in both sexes.